The United States has specific standards of the amount of electronic voltage used in buildings and devices. These are to ensure all electronic devices made for American use receive the correct amount of power in a safe and consistent manner. These standards are used in other North American countries, such as Canada and Mexico, as well.
Buildings in the United Sates are wired at a voltage of 210 volts alternating current, which is set by the National Electrical Manufacturers Association. This voltage connector requires a NEMA plug, a two-pronged plug with the prongs 1/4 inch wide (one is slightly wider to identify the neutral plug) and 0.06 inches thick. Plugs with only these two prongs are NEMA 1; a NEMA 5 plug includes a third rounded prong as a grounding plug.
Automotive batteries that supply electricity to cars are usually set at 12.6 volts. This voltage ensures the battery has enough juice to start the engine when cranking. An automotive battery is usually a lead acid battery containing six galvanic cells, each containing 2.1 volts. Many cars are equipped to power other electronic devices using the battery, but these devices need a 12-volt direct-current connector. This connector is a cylindrical shape with one central prong 1/2 inch in diameter. This connector was originally designed to light cigarettes, and there are other connector styles for 12-volt DC power, but this is the common style for vehicles.
Dry Cell Batteries
Most standard batteries supply 1.5 volts apiece and come in four main cylindrical sizes. The most common type is AA; these batteries are 2 inches long and about 1/2 inch in diameter. A AAA battery is 1 3/4 inches long and less than a half inch in diameter. A C battery is about 2 inches long and a little over an inch in diameter, while a D battery is about 1 1/2 inches in diameter. There are also 9-volt batteries, which are rectangular-shaped and measure 1.8 by 1 by 0.6 inches. Unlike the other dry cells, which have the positive and negative terminals on opposite ends, 9-volts have both terminals on the top end.
Anyone with electronic devices that use nonstandard voltage connectors for the United States will need an adapter that functions as an electronic bridge between the two connections. Any device whose DC power is less than 120 volts, such as a radio that takes three AA batteries --- should come with a special adapter plug. In addition, you need a special converter to connect a 120-volt plug into a 12-volt power supply. The most common way to do this is with a power inverter that connects to the car battery --- either by plugging it into the aforementioned socket or wiring it directly to the battery terminals --- and converts the 12-volt DC power into 120-volt AC power.
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